If df = pd.read_csv('file.txt', sep='\t') returns a DataFrame with one column, then apparently file.txt is not using tabs as separators. Your data might simply have spaces as separators. In that case you could try

df = pd.read_csv('data', sep=r'\s{2,}')

which uses the regex pattern \s{2,} as the separator. This regex matches 2-or-more whitespace characters.